add k8s version strategy

Although there is a version strategy for github, whereby the latest version is resolved via the gh release pages something similar did not exist for k8s releases.

https://cdn.dl.k8s.io/release/stable.txt is made available to enable resolution of the latest version.

This change integrates functionality that interrogates this file and uses its contents to assert the version of `kubectl` to retrieve.  This will negate the situation described in #1048 where the version is out of date until the `arkade` code is updated.

Signed-off-by: Richard Gee <richard@technologee.co.uk>

pkg/get/get.go

@@ -17,6 +17,9 @@ import (
 	"github.com/alexellis/arkade/pkg/env"
 )
 
+const GitHubVersionStrategy = "github"
+const k8sVersionStrategy = "k8s"
+
 var supportedOS = [...]string{"linux", "darwin", "ming"}
 var supportedArchitectures = [...]string{"x86_64", "arm", "amd64", "armv6l", "armv7l", "arm64", "aarch64"}
 
@@ -139,22 +142,34 @@ func (tool Tool) Head(uri string) (int, string, http.Header, error) {
 
 func (tool Tool) GetURL(os, arch, version string, quiet bool) (string, error) {
 
-	if len(version) == 0 &&
-		(len(tool.URLTemplate) == 0 ||
-			strings.Contains(tool.URLTemplate, "https://github.com/") ||
-			tool.VersionStrategy == "github") {
+	if len(version) == 0 {
+
 		if !quiet {
 			log.Printf("Looking up version for %s", tool.Name)
 		}
 
-		v, err := FindGitHubRelease(tool.Owner, tool.Repo)
-		if err != nil {
-			return "", err
+		if len(tool.URLTemplate) == 0 ||
+			strings.Contains(tool.URLTemplate, "https://github.com/") ||
+			tool.VersionStrategy == GitHubVersionStrategy {
+
+			v, err := FindGitHubRelease(tool.Owner, tool.Repo)
+			if err != nil {
+				return "", err
+			}
+			version = v
 		}
+
+		if tool.VersionStrategy == k8sVersionStrategy {
+			v, err := FindK8sRelease()
+			if err != nil {
+				return "", err
+			}
+			version = v
+		}
+
 		if !quiet {
-			log.Printf("Found: %s", v)
+			log.Printf("Found: %s", version)
 		}
-		version = v
 	}
 
 	if len(tool.URLTemplate) > 0 {
@@ -230,6 +245,41 @@ func FindGitHubRelease(owner, repo string) (string, error) {
 	return version, nil
 }
 
+func FindK8sRelease() (string, error) {
+	url := "https://cdn.dl.k8s.io/release/stable.txt"
+
+	timeout := time.Second * 5
+	client := makeHTTPClient(&timeout, false)
+	client.CheckRedirect = func(req *http.Request, via []*http.Request) error {
+		return http.ErrUseLastResponse
+	}
+
+	req, err := http.NewRequest(http.MethodGet, url, nil)
+	if err != nil {
+		return "", err
+	}
+
+	req.Header.Set("User-Agent", pkg.UserAgent())
+
+	res, err := client.Do(req)
+	if err != nil {
+		return "", err
+	}
+
+	if res.Body == nil {
+		return "", fmt.Errorf("unable to determine release of tool")
+	}
+
+	defer res.Body.Close()
+	bodyBytes, err := io.ReadAll(res.Body)
+	if err != nil {
+		return "", err
+	}
+
+	version := string(bodyBytes)
+	return version, nil
+}
+
 func getBinaryURL(owner, repo, version, downloadName string) string {
 	if in := strings.Index(downloadName, "/"); in > -1 {
 		return fmt.Sprintf(

pkg/get/get_test.go

@@ -36,6 +36,40 @@ func getTool(name string, tools []Tool) *Tool {
 	return tool
 }
 
+func TestGetToolVersion(t *testing.T) {
+
+	testCases := []struct {
+		description string
+		tool        Tool
+		version     string
+		expected    string
+	}{
+		{
+			description: "Version is empty, expect the tool's version to be returned",
+			tool:        Tool{Version: "1.0.0"},
+			version:     "",
+			expected:    "1.0.0",
+		},
+		{
+			description: "Version argument is provided, expect the provided version to be returned",
+			tool:        Tool{Version: "2.0.0"},
+			version:     "1.2.0",
+			expected:    "1.2.0",
+		},
+	}
+
+	// Iterate over test cases
+	for _, tc := range testCases {
+		// Call the function with test inputs
+		result := GetToolVersion(&tc.tool, tc.version)
+
+		// Check if the result matches the expected output
+		if result != tc.expected {
+			t.Errorf("%s: For tool version %s and input version %s, expected %s but got %s", tc.description, tc.tool.Version, tc.version, tc.expected, result)
+		}
+	}
+}
+
 func Test_MakeSureNoDuplicates(t *testing.T) {
 	count := map[string]int{}
 	tools := MakeTools()

pkg/get/tools.go

@@ -54,7 +54,7 @@ func MakeTools() Tools {
 			Owner:           "helm",
 			Repo:            "helm",
 			Name:            "helm",
-			VersionStrategy: "github",
+			VersionStrategy: GitHubVersionStrategy,
 			Description:     "The Kubernetes Package Manager: Think of it like apt/yum/homebrew for Kubernetes.",
 			URLTemplate: `
 						{{$os := .OS}}
@@ -150,11 +150,11 @@ func MakeTools() Tools {
 	// https://dl.k8s.io/release/v1.22.2/bin/darwin/amd64/kubectl
 	tools = append(tools,
 		Tool{
-			Owner:       "kubernetes",
-			Repo:        "kubernetes",
-			Name:        "kubectl",
-			Version:     "v1.29.2",
-			Description: "Run commands against Kubernetes clusters",
+			Owner:           "kubernetes",
+			Repo:            "kubernetes",
+			Name:            "kubectl",
+			VersionStrategy: k8sVersionStrategy,
+			Description:     "Run commands against Kubernetes clusters",
 			URLTemplate: `{{$arch := "arm"}}
 
 {{- if eq .Arch "x86_64" -}}